A phased-array radar system can include a large number of (e.g. several thousand) modules that each include a phase shifter leading to an amplifier which leads to an antenna. By maintaining a selected phase shift for each of the numerous modules, the radar can direct and receive a beam along a selected direction, with very low side lobes. It is desirable to minimize side lobes in transmission to minimize wasted power, and it is especially important to minimize side lobes in reception to minimize the effect of any extraneous noise such as from a jammer that transmits unwanted radar signals.
One type of phase shifter used in each module includes several phase shift devices of progressively greater phase shift angles, which are coupled to locations spaced along a conductor that carries a radar signal. Depending upon which of the shift devices is switched on, any one of a large number of total phase shifts can be achieved. Such a phase shifter may include a few loaded line type phase shifters that can each produce a phase shift of less than 90.degree., plus one or more reflection type phase shifters that can each produce a phase shift of 90.degree. or a multiple thereof. The reflection type wave shifters have a low VSWR (voltage standing wave ratio), while the loaded line type phase shifters produce higher VSWR with the amount increasing for devices that produce greater phase shifts. A phase shifter which minimized the VSWR resulting from a loaded line type phase shift device of large phase shift such as at least 30.degree., would reduce the overall VSWR of the phase shifter.
In a phase shifter having a particular number of phase shift devices, each device may produce a phase shift one-half of the previous device, so that the total phase shift can be increased in minimal steps with the least number of phase shift devices. For example, in a five bit phase shifter, the five devices may each produce phase shifts of 11.25.degree., 22.5.degree., 45.degree., 90.degree., and 180.degree.. Where the devices are formed on a single chip, such as of galium arsenide, the phase shift produced by any device will typically vary by up to about 2.degree. to 3.degree. from the nominal level. It is difficult to compensate for such errors, especially since the total phase shift error depends upon the particular combination of phase shift devices which are activated and the particular error of each device. A phase shifter which included easily set means for correcting the effect of errors in the phase shifts of the shifter devices, would be of considerable value.